Global emergency declared as polio cases surge

By Debora MacKenzie

For only the second time in its history, the World Health Organization has declared a Public Health Emergency of International Concern (PHEIC). The threat is an upsurge of polio, even as the world comes close to eradicating the virus. In response, vaccination drives will be stepped up, while authorities try to ensure that people in 10 countries who want to travel internationally have been vaccinated in the previous 12 months.

The declaration follows a week-long consultation among global polio experts triggered by a worrying surge in cases during 2014, even though it has so far been the low season for the disease, which attacks the nervous system and can cause paralysis. Polio primarily spreads through contaminated water supplies, and with the warmth and rains of spring in the northern hemisphere, the high season starts in the next few weeks.

The WHO’s 2005 International Health Regulations call for a PHEIC declaration when international coordination is required to meet a health threat. The only other time WHO has declared one was early in the swine flu pandemic of 2009, when the virus’s severity was not yet known.

Concern that one would be needed for polio has been mounting since January, as war and unrest in several countries have interrupted vaccination. “If the situation as of today went unchecked, it could result in failure to eradicate,” says Bruce Aylward, head of polio at WHO.

Cases on the rise

The most recent numbers speak for themselves. By last year at this time, there had been only 24 cases worldwide of disease caused by wild polio virus, representing only 6 per cent of the 417 cases eventually diagnosed last year. This year there have already been 68 cases, meaning numbers could now rise much higher. Nine of those were in five countries which had no known cases last year.

Polio currently circulates constantly in only three countries: Pakistan, Nigeria and Afghanistan. The biggest problem is Pakistan, home of 59 of this year’s 68 cases, where some polio vaccinators have been shot by political dissidents. Pakistan is now quelling the scourge, says Aylward, with massive security and bans on motorcycles during vaccination drives to reduce the threat of drive-by shootings.

Genetic sequencing shows the virus is travelling, however. Pakistan has exported it to Afghanistan this year, and to Israel, Egypt, Syria and China over the past two years. To try and stop such movement, the WHO has asked Pakistan – as well as Syria and Cameroon, which have also exported the virus this year – to “ensure” that any resident travelling outside the country has had a dose of polio vaccine in the preceding year.

The WHO will watch for exported cases in a bid to ensure the rules are being applied, says Aylward – more stringent recommendations could follow if they are not.

Low immunity

Pakistan has already set up vaccination booths at its land border crossings. It was mostly vaccinating children there, says Aylward, but now it will start vaccinating adults as well. Last year 60 per cent of polio cases resulted from international spread, and much of it was carried by adults.

This is because polio causes disease in only one to five people out of every 1000 who encounter it for the first time; everyone else becomes immune. With polio now gone from much of the world, such natural exposure and immunisation has largely stopped. Meanwhile vaccine-derived immunity is falling, as people neglect to get boosters for long-ago childhood vaccinations, or increasingly were never vaccinated for polio.

That is the ultimate reason for this week’s emergency, epidemiologists say. With immunity at an all-time low worldwide, any return of polio now could be horrific.